I had this problem when I tried to use a mission expression pedal, ( not the helix brand one, a mate lent me one of there others) I’m sorry to say I never found a fix. I went back to my old ex-1 and I have had no problems. I don’t know if maybe the travel is too far For it to read or if it’s something more technical. I have seen these complaints across the net though. It seems some pedals just don’t work properly with helix family units.
there where a couple of older threads on here somewhere where people have recommendations.